Random Hacks comments

"Screencast: Use Rails and RDF.rb to parse Best Buy product reviews" by Gregg Kellogg

Wed, 08 Jun 2011 17:24:18 +0000

Great demo Eric! For another take on parsing Best Buy data, use http://rdf.greggkellogg.net/distiller (source available on GitHub as rdf-portal), also using the RDF.rb gems, to generate HTML+RDFa (or any other serialization) marked up with the same information as the search requests.

Also, we do have SPARQL support, but not in the released versions yet. Check out http://github.org/gkellogg/sparql-grammar, which uses the 0.4.x tag of RDF.rb to provide full SPARQL 1.0 support natively in Ruby.

Thanks for the great work and helping to show what a great environment for working with RDF Ruby really is.

Gregg

"Derivatives of algebraic data structures: An excellent tutorial" by Frank Atanassow

Tue, 24 May 2011 20:30:41 +0000

@Eric I beg to differ. The article starts, “With the spreading popularity of languages like F# and Haskell, many people are encountering the concept of an algebraic data type for the first time. When that term is produced without explanation, it almost invariably becomes a source of confusion. In what sense are data types algebraic?”

So whereas they claim to explain in what sense an adt is algebraic, what they end up explaining is in what sense the kind * is algebraic.

"Derivatives of algebraic data structures: An excellent tutorial" by Eric

Mon, 23 May 2011 13:04:02 +0000

Aleksey, Steve: Thank you! I fixed the link.

Frank: Surely, among consenting category theorists, all isomorphic objects are identical. ;-) Thank you for the correction.

The article isn’t trying to explain algebraic data types by an analogy to differention. Rather, it’s trying to explain type differentiation, and it needs to define a loose algebra of types to get there.

"Derivatives of algebraic data structures: An excellent tutorial" by Steve Massey

Sun, 22 May 2011 10:42:48 +0000

This is the same paper:

http://strictlypositive.org/Dissect.pdf

"Derivatives of algebraic data structures: An excellent tutorial" by Aleksey Khudyakov

Sat, 21 May 2011 14:08:02 +0000

This link leads to 403 page. Is this paper available anywhere else?

http://www.cs.nott.ac.uk/~ctm/Dissect.pdf

"Derivatives of algebraic data structures: An excellent tutorial" by Frank Atanassow

Fri, 20 May 2011 23:47:27 +0000

I only read the first half, and it looks like a nice tutorial, but it does not explain what it claims to explain, namely in what sense adt’s are algebraic.

Algebraic datatypes are not called algebraic because type constructors form an algebra, but rather because data constructors do. In fact, type constructors do not even form an algebra; they form a pseudo-algebra, which is a generalization of algebras. That is why properties like associativity of products only hold up to (unique, natural) isomorphism rather than up to type equality.

If you want to explain the algebraic nature of Haskell datatypes with an allusion to differentiation, you can do it by defining a datatype, say, of polynomials.

"What do these fixed points have in common?" by Eric

Thu, 12 May 2011 17:24:18 +0000

Thank you for the pointer! I’ll try to dig up those papers when I have time to play with this stuff a bit.

Some related links of interest:

1. The Wikipedia article on fixed-point theorems.

2. A MathOverflow question about the relation between two of the big fixed-point theorems.

Nash equilibria can apparently be derived from Brouwer fixed points, according to Wikipedia, but I haven’t read the proof yet.

"What do these fixed points have in common?" by Derek Elkins

Thu, 12 May 2011 17:02:07 +0000

There’s a “small” (categorical) diagram that is rarely talked about that is relevant here. The popular examples are empty diagrams, finite diagrams of discrete points, parallel pairs of arrows, and wedges. The colimits of those are, respectively, initial objects, coproducts, coequalizers, and pushouts. There is another notable diagram however, the loop. Barry Jay has a couple of papers on the limits and colimits of a diagram of this form. I don’t know if this will capture all of these examples (in particular, the Nash equilibria would take a bit of twisting I’d think), but it certainly is a place to start.

"AWS outage timeline & downtimes by recovery strategy" by Eric

Mon, 25 Apr 2011 19:44:49 +0000

The links should be fixed. Thanks, linkchecker!

"AWS outage timeline & downtimes by recovery strategy" by linkchecker

Mon, 25 Apr 2011 16:56:45 +0000

Under “Lessons Learned”, #3, both links point to the reddit blog. Presumably one should point to Netflix instead.